Data bus systems are widely used for delivering data communications from one or more source entities to selected ones of a plurality of destination entities which are relatively close in proximity to the source entities. To deliver a data communication to a particular destination in a typical bus system, a source entity will accompany the communication with address code designating the desired destination and then direct the address code and the data to the bus for distribution in parallel to all the destinations on the bus. The addressee destination entity, upon identifying its own address code on the bus, accepts the data and advantageously returns an acknowledgement to the sender that the communication has been accepted.
A bus system of the above-described type is disclosed in a communication processing system described in the application of G. R. Babecki et al, Ser. No. 393,111 filed June 28, 1982. The communication processing system in accordance with the Babecki et al disclosure comprises a plurality of nodes communicating by way of a common carrier communication system. Each node contains a plurality of communication processors and a data base processor, all such processors being interconnected by way of a data bus. Each of the processors have interfacing capability to deliver data communications to the bus and thus act as a source entity and to accept data communication from the bus and thus act as a destination entity. In a communication processing system of this type, it is important to insure that these various processors are capable of interchanging data communication in order to preserve the overall capability of the communication processing system. It is a broad object of the present invention to provide a data bus system which insures delivery of data communications.
It is well known to provide redundant bus systems to insure delivery of data communications. In one type of redundant systems, two or more bus systems are provided wherein each of the bus systems might normally provide all or a portion of the deliveries and the other bus system is on standby, prepared to handle the deliveries in the event that the "active" bus system should fail to deliver data communications due, for example, to a failure of a bus system component or input/output equipment interfacing the bus system. In such an event, the standby bus would "take over" and thereafter provide the communication deliveries normally provided by the failed bus system ( in addition to the deliveries that the standby might normally provide). These redundant systems require that each "standby" bus or buses carry all its own normal traffic and all of the traffic normally carried by the "failed" bus. In the event of such failure, the additional traffic might overburden the resources of the standby bus. It is therefore an object of this invention to reduce the additional traffic carrying capacity requirements imposed on the standby bus when the "active" bus "fails" in a redundant bus system.